Radio communication system

ABSTRACT

A transmission apparatus in a radio communication system which simultaneously uses a plurality of different radio frequencies to transmit signals. The apparatus includes a radio format setting portion, which is provided for each transmission frequency of the plurality of different radio frequencies and separately sets a radio format of transmission signals for each transmission frequency; and a transmitter, which is provided for each transmission frequency of the plurality of different radio frequencies and transmits signals at each of said transmission frequencies. Each radio format setting portion sets a pilot length of the transmission signals separately for each transmission frequency of the plurality of different radio frequencies.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Divisional Application of U.S. application Ser.No. 11/819,410, filed on Jun. 27, 2007, now pending, which is acontinuation of International Patent Application PCT/JP2005/000057,filed Jan. 6, 2005, the contents of each are herein wholly incorporatedby reference.

BACKGROUND OF THE INVENTION

The present invention relates to a radio communication system which usesmultiple bands or a plurality of different radio frequencies, and inparticular relates to a radio communication system, and a transmissionapparatus and reception apparatus, which use different radiotransmission methods (radio transmission parameters) for each band orradio frequency.

Second-generation mobile telephone systems use a plurality of frequencybands, such as the 800 MHz band and the 1.5 GHz band. And, in theIMT-2000 third-generation mobile telephone system, currently the 2 GHzband is being used, but usage of the 800 MHz band in the near future isalso being studied. Thus the use of a plurality of frequency bands in asingle mobile telephone system is a well-known fact.

In a multiple-band radio communication system, that is, a radiocommunication system using a plurality of bandwidths (bands), or in amulti-carrier radio communication system using a plurality of differentradio frequencies, in the prior art the same radio parameters which aresynonyms of the radio formats were used for all. That is, the radioformat comprises, for example, (1) the length of interpolated pilotsnecessary for channel estimation, (2) the length of the guard intervalGI to prevent intersymbol interference, and (3) the number ofsubcarriers in multi-carrier transmission and the interval betweensubcarriers; in the prior art, these radio parameters (formats) were thesame regardless of the radio frequency or band. However, if thefrequency band used is different, then propagation characteristics aredifferent, and so reception performance is accordingly different. FIG.15 explains multi-band transmission; in order to simplify theexplanation, the frequency bands are limited to the 1 GHz band and the 2GHz band, but there is no need to limit the bands to these frequencybands, nor is there a need to limit transmission to two bands.

(1) Radio transmission system with pilot interpolation:

In a radio transmission system in which the 1 GHz and 2 GHz frequencybands are used, even when the motion velocity is the same, one fadingvelocity is twice the other due to the frequency bands used. Hence ifthe pilots of the same length are interpolated for channel estimation,the channel estimation precision will be different for 1 GHz and for 2GHz, and reception performance will be poorer in the 2 GHz band comparedwith the 1 GHz band. However, in the prior art, as shown in FIG. 16, thelengths of the pilots PL1, PL2 interpolated into the data DT1, DT2regardless of frequency band are the same, and so there has been theproblem that the channel estimation precision is worsened for the 2 GHzband.

FIG. 17 shows the configuration of such a transmission apparatus of theprior art, in which the pilot length is held constant regardless of thefrequency band; FIG. 18 shows the configuration of a receptionapparatus.

In the transmission apparatus, the modulation portion 1 a performs forexample QPSK modulation of the transmission data, the pilot insertionportion 1 b inserts pilot signals PL into the QPSK in-phase componentand quadrature component, the 1 GHz transmitter 1 c up-converts thefrequency of signals with pilots PL to 1 GHz and transmits the signals,and the 2 GHz transmitter 1 d up-converts the frequency of the signalswith pilots PL inserted to 2 GHz and transmits the signals. Pilotinsertion may be performed before QPSK modulation.

In the reception apparatus, the 1 GHz receiver 2 a down-convertsreceived 1 GHz high-frequency signals to baseband signals and inputs thesignals to the selection portion 2 c, and the 2 GHz receiver 2 bdown-converts received 2 GHz high-frequency signals to baseband signalsand inputs the signals to the selection portion 2 c. The selectionportion 2 c selects baseband signals output from the receiver indicatedby a 1 GHz/2 GHz selection signal SEL output from a control portion, notshown, and inputs these signals to the pilot extraction portion 2 d anddemodulation portion 2 e. The pilot extraction portion 2 d extractspilots from the input signals, and the channel estimation portion 2 fuses the extracted pilot signals and known pilot signals to estimate thechannel (path propagation characteristics). The demodulation portion 2 eperforms channel compensation of data signals based on the channelestimation value, and then demodulates the transmission data.

In this way, the transmission apparatus inserts pilot signals of thesame length for both 1 GHz/2 GHz, and uses the same radio format totransmit the radio signals. Hence when demodulating data transmitted at2 GHz, the channel estimation precision is worsened, and sohigh-precision data demodulation is not possible.

(2) Radio transmission system with guard intervals inserted:

In a radio transmission system in which guard intervals GI are insertedin order to prevent intersymbol interference, the necessary guardinterval length differs depending on the positional relation between thebase station and the mobile station. For example, propagation lossesdiffer at 1 GHz and at 2 GHz, and it is known that signals reach fartherat 1 GHz, and the delay spread is longer in the 1 GHz band. The guardinterval length is generally determined according to the longest delayspread. That is, when the guard interval length is the same (same radioformat) for each band, the positional relation between base station andmobile station for which the delay spread is longest is assumed todetermine the required guard interval length. FIG. 19 is an example of aradio format of the prior art; the length of 1 GHz/2 GHz guard intervalsGI is determined based on 1 GHz delay spreading. From the above, in the2 GHz band the guard intervals are too long, that is, there is theproblem that transmission efficiency is worsened by providing excessguard interval length.

FIG. 20 is an example of a transmission apparatus in a radiotransmission system in which guard intervals GIs are the same; FIG. 21shows the configuration of a reception apparatus, in an example ofmulticarrier transmission by Orthogonal Frequency Division Multiplexing(OFDM), in which data is transmitted from a transmitter with guardintervals of the same length inserted at 1 GHz/2 GHz.

In the transmission apparatus, the serial/parallel conversion portion 3a _(i) of the multicarrier modulation portion 3 a converts thetransmission data into N parallel data symbols, the IFFT portion 3 a ₂performs IFFT processing of the parallel data symbols into N subcarriercomponents, and the parallel/serial conversion portion 3 a ₃ convertsthe N-symbol IFFT processing result into serial data, which is output.The guard interval addition portion 3 b adds a guard interval ofconstant length, set in advance, to the beginning of N-symbols, the 1GHz transmitter 3 c up-converts the frequency of the signals with guardintervals inserted to 1 GHz and transmits the signals, and the 2 GHztransmitter 3 d up-converts the frequency of the signals with guardintervals inserted to 2 GHz and transmits the signals.

In the receiver, the 1 GHs receiver 4 a down-converts the 1 GHzhigh-frequency received signals to baseband signals and inputs thesignals to the selection portion 4 c, and the 2 GHz receiver 4 bsimilarly down-converts 2 GHz high-frequency received signals tobaseband signals and inputs the signals to the selection portion 4 c.The selection portion 4 c selects baseband signals output from thereceiver indicated by a 1 GHz/2 GHz selection signal SEL output from acontrol portion, not shown, and inputs these signals to the guardinterval removal portion 4 d. The guard interval removal portion 4 dremoves guard intervals from the input signals, and inputs the result tothe FFT portion 4 e. The FFT portion 4 e parallel-converts the inputsignals into N-symbols, then performs N-point FFT processing,serial-converts the FFT result, and inputs this to the demodulationportion 4 f. The demodulation portion 4 f demodulates the transmissiondata from the input signals.

In this way, the transmitter inserts guard intervals of the same length,and uses the same radio format for transmission of radio signals at both1 GHz/2 GHz. As a result, the guard intervals are too long at 2 GHz, andtransmission efficiency is worsened.

(3) Multicarrier transmission system using multiple bands:

As shown in FIG. 22, in radio communication systems which performmulticarrier transmission by the OFDM method in each of multiple bands(the 1 GHz band and 2 GHz band), when frequency fluctuations due tofading occur, the orthogonality between adjacent subcarriers isdegraded. The degree of degradation of orthogonality differs with thefrequency band used. That is, even when the motion velocity is the same,in the 2 GHz band the amount of frequency fluctuation is twice that inthe 1 GHz band, and so the amount of degradation is greater than in the1 GHz band.

In OFDM, transmission signals are serial/parallel-converted (convertedinto N parallel signals), the signal rate is lowered, and the Ntransmission signals are each allocated to a subcarrier and transmitted.The subcarrier interval or band width is determined by the signal rate(=1/T Hz) after serial/parallel conversion. Subcarrier intervals are setto 1/2 T intervals so that subcarriers are orthogonal on the frequencyaxis. In this OFDM transmission method, as explained above, there isfrequency fluctuation due to multipath fading, and when theorthogonality between subcarriers is degraded, performance deteriorates.Hence there is a need to set the frequency intervals in advance takingthis fluctuation into account, so that degradation in a band does notoccur. However, In multiple-band radio transmission systems of the priorart, subcarrier intervals in a band are the same at 1 GHz and at 2 GHz.A radio communication system performing multicarrier transmission usingOFDM in multiple bands (the 1 GHz band and 2 GHz band) has the sameconfiguration as in FIG. 20 and FIG. 21.

There exists technology in which, when the degree of signal degradationdiffers with the frequency, signals for a frequency channel with asatisfactory reception state are selectively received (JP 2002-64458A).In this technology of the prior art, in a multi-frequency network inwhich a plurality of transmitting stations transmit the same content atdifferent frequencies, a receiving station detects the reception levelsof signals sent over two channels with different frequencies, and usesthe signals in the channel with the higher reception level for contentrestoration.

Also, there exists technology in which a frequency, time, or directionfor which radio communication interference is anticipated is determined,and radio communication is performed avoiding these conditions (JP2002-300172A).

However, these technologies of the prior art do not improve thereception performance in each band or at each frequency in amultiple-band radio communication system or in a multicarrier radiocommunication system.

SUMMARY OF THE INVENTION

In light of the above, an object of the invention is, in a multiple-bandradio communication system and a multicarrier radio communicationsystem, to improve the reception performance, and moreover thetransmission efficiency, in each band or at each frequency.

A further object of the invention is to improve the channel estimationprecision and improve the reception performance at each frequency, andenhance transmission efficiency, by changing the lengths of pilotsinserted at each frequency.

A further object of the invention is to reduce intersymbol interferenceand improve reception performance in each band or at each frequency, andenhance transmission efficiency, by changing the lengths of guardintervals inserted in each band or at each frequency.

A further object of the invention is to reduce the effect of frequencyfluctuations and improve reception performance in each band, and enhancetransmission efficiency, by using different numbers of subcarriers inmulticarrier transmission, or different subcarrier intervals, in eachband.

This invention relates to a radio communication system which usesmultiple bands or a plurality of different radio frequencies (forexample, two non-continuous bands, two separated bands, two radiofrequencies belonging to different frequency bands, or similar); in thisradio communication system, different radio transmission parameters(transmission methods) are used in each of the bands or at each of theradio frequencies. That is, by transmitting data using different radioparameters (radio formats) in each band or at each radio frequency, theradio transmission methods are made different in each band or at eachradio frequency.

Here, even in a case where data is transmitted using different radioparameters for each band for only two bands among a plurality of bands,it can be interpreted that a communication system uses different radiotransmission parameters for each of two used bands. Of course, differentradio transmission parameters can be used for all of the bands used aswell.

Further, when parameters are made different, it is preferable that theparameters be made different in common for radio communicationapparatuses (radio transmission apparatuses and radio receptionapparatuses) which use same band. For example, radio communicationapparatuses which communicate using a first band, uniformly use thefirst parameter applied to the first band, and radio communicationapparatuses which communicate using a second band, uniformly use thesecond parameters applied to the second band.

When a radio communication apparatus is instructed, by external input orsimilar, to use a first band or a second band, it is desirable that theparameters corresponding to the respective bands be read from a storageportion, and that a control portion execute control of various portionsaccording to the read-out parameters.

Of course, when one radio communication apparatus accommodates only asingle band, it is desirable that other radio communication apparatusesuse a different band and that parameters compatible with the first bandand parameters compatible with the second band respectively be used. Inthis case, it is again desirable that radio parameters corresponding toeach band be stored in a storage portion, in order that each radiocommunication apparatus can accommodate any band, and that the controlportion read radio parameters according to a specified band and executecontrol.

Further, when using three different bands, which are first, second, andthird bands (assuming that the frequency interval between the secondband and third band is greater than the frequency interval between thefirst band and second band), the same radio parameters can be used inthe first and second bands, and different radio parameters can be usedin the third bands. By this means, portions in which problems arisingdue to different frequencies appear prominently can be targeted andaddressed and the problem can be removed.

Further, it is preferable that radio communication apparatuses using afirst band and a second band be a single radio communication apparatus(radio base station), but may be different radio communicationapparatuses.

When different radio communication apparatuses use both the first andsecond bands, it is desirable that the apparatuses belong to the samecommunication carrier, or adopt the same radio communication method (forexample OFDM) other than parameters described below, or belong to thesame radio communication system (for example a fourth-generation mobilecommunication system), or have a common core network.

Of course, if the radio parameters described below are made different,then the first band may belong to a first communication carrier and thesecond band to a second communication carrier.

Further, for the radio communication apparatuses using a first band anda second band, it is desirable that the same coding method, decodingmethod, and modulation/demodulation method be adopted, but that in radiosegments the radio format for transmission and reception (for example,the formats described below) be made different. A first specific methodin which radio parameters (radio formats) are made different is a methodin which pilot lengths are made different in each band or at each radiofrequency. By this means, the channel estimation precision at eachfrequency can be improved, and reception performance and transmissionefficiency can be enhanced.

A second specific method in which radio parameters (radio formats) aremade different is a method in which pilot intervals are made differentin each band or at each radio frequency. By this means, the channelestimation precision is improved at each frequency, and receptionperformance and transmission efficiency can be enhanced.

A third specific method in which radio parameters (radio formats) aremade different is a method in which guard interval lengths are madedifferent in each band or at each radio frequency. By this means,intersymbol interference is reduced at each frequency, and receptionperformance and transmission efficiency can be enhanced.

A fourth specific method in which radio parameters (radio formats) aremade different is a method in which, when multicarrier modulation isused for radio communication in each band, the number of subcarriers ofmulticarrier transmission are made different, or the subcarrierintervals are made different, in each band. By this means, the effect offrequency fluctuations in each band is reduced, and receptionperformance and transmission efficiency can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first drawing explaining the principle of a first embodimentin which pilot lengths are made different at each radio frequency, in aradio communication system using a plurality of different radiofrequencies;

FIG. 2 is a second drawing explaining the principle of the firstembodiment in which pilot lengths are made different at each radiofrequency, in a radio communication system using a plurality ofdifferent radio frequencies;

FIG. 3 is a drawing explaining the principle of a second embodiment inwhich guard interval lengths are made different in each band or at eachradio frequency;

FIG. 4 is a drawing explaining the principle of a third embodiment inwhich, when multicarrier modulation is used in radio communication ineach band, the number of subcarriers in multicarrier transmission ismade different, or the subcarrier interval is made different, in eachband;

FIG. 5 explains the fact that by increasing subcarrier intervals, theeffect of frequency fluctuations can be reduced;

FIG. 6 shows the configuration of a transmission apparatus in the firstembodiment, in which the pilot length is made different at each radiofrequency in a radio communication system using a plurality of differentradio frequencies;

FIG. 7 shows the configuration of a reception apparatus in the firstembodiment;

FIG. 8 shows another configuration of a reception apparatus in the firstembodiment;

FIG. 9 shows the configuration of a transmission apparatus in the secondembodiment, in which the guard interval length is made different in eachband, in a radio communication system which performs OFDM transmissionin each of a plurality of bands;

FIG. 10 shows the configuration of a reception apparatus in the secondembodiment;

FIG. 11 shows another configuration of a transmission apparatus in thesecond embodiment;

FIG. 12 shows still another configuration of a transmission apparatus inthe second embodiment;

FIG. 13 shows the configuration of a transmission apparatus in a thirdembodiment, in which the number of subcarriers is made different and thesubcarrier interval is made different in each band, in a radiocommunication system performing OFDM transmission in each of a pluralityof bands;

FIG. 14 shows the configuration of a reception apparatus in the thirdembodiment;

FIG. 15 explains multiple-band transmission;

FIG. 16 explains an example of the prior art, in which the lengths ofpilots PL1, PL2 inserted into data are made the same length regardlessof the frequency band;

FIG. 17 shows the configuration of a transmission apparatus when pilotlengths are held constant regardless of the frequency band in the priorart;

FIG. 18 shows the configuration of a reception apparatus when pilotlengths are held constant regardless of the frequency band in the priorart;

FIG. 19 explains an example of the prior art, in a case where guardinterval lengths are held constant regardless of the frequency band;

FIG. 20 shows the configuration of a transmission apparatus in a casewhere guard interval lengths are held constant regardless of thefrequency band;

FIG. 21 shows the configuration of a reception apparatus in a case whereguard interval lengths are held constant regardless of the frequencyband; and,

FIG. 22 explains the fact that the degree of degradation oforthogonality differs with the frequency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) Summary of the Invention

A principle of the invention is making the radio parameters (radioformats) used in each band of a plurality of bands, or at each frequencyin multicarrier transmission, compatible with the frequency band.

Of course, as explained in the disclosure of the invention, there is noneed to make such parameters compatible for all bands used; it issufficient to make parameters compatible with at least two bands.

However, it is desirable that radio parameters be made compatible withall of the bands used.

A first method for making the radio parameters compatible with thefrequency bands, in a radio communication system where a plurality ofbands (for example, two separated bands, non-continuous bands, andsimilar) or a plurality of different radio frequencies (for example, tworadio frequencies belonging to different bands, or similar) are used, isto make pilot lengths different in each band or at each radio frequency.By this means, the channel estimation precision is improved andreception performance can be improved in each band or at each frequency.In order to make pilot lengths different, as shown in FIG. 1, theinsertion interval of interpolation pilots PL2 in the 2 GHz band is madey/2, as opposed to an insertion interval of y for interpolation pilotsPL1 in the 1 GHz band. When estimating the propagation path,interpolation pilots are used, and when the insertion interval is madedense, the precision of estimation can be raised.

Another method of making pilot lengths different is to make theinterpolation pilot length in the 2 GHz band twice the interpolationpilot length x in the 1 GHz band, as shown in FIG. 2. By this means,similarly to the case of FIG. 1, the estimation precision can be raised.

A second method for making the radio parameters compatible with thefrequency bands is to make the guard interval lengths different in eachband or at each radio frequency. By this means, intersymbol interferencecan be reduced, and reception performance improved, in each band or ateach frequency. That is, as shown in FIG. 3, guard interval lengths areprepared which are different in each band or at each frequency, and theshortest guard interval length is allocated to the highest-frequencyband (2 GHz), while the longest guard interval length is allocated tothe lowest-frequency band (1 GHz). This is because the higher thefrequency, the shorter is the propagation distance, so that delay spreadis also shorter. By using a radio parameter with a short guard intervallength for a mobile station in a position in which the delay spread isshort, transmission efficiency can be improved.

A third method for making the radio parameters compatible with thefrequency bands is, when using multicarrier modulation for radiocommunication in each band, to make the number of subcarriers inmulticarrier transmission different in each band, or to make thesubcarrier intervals different. By this means, the effect of frequencyfluctuations in each band can be reduced, reception performance can beimproved, and transmission efficiency can be enhanced. That is, as shownin FIG. 4, by making the number of subcarriers M in the 2 GHz bandsmaller than the number of subcarriers N in the 1 GHz band (M<N),subcarrier intervals in the 2 GHz band are larger than in the 1 GHzband. By this means, the effect of frequency fluctuations in each bandcan be reduced, reception performance is improved, and transmissionfrequency can be enhanced.

FIG. 5 explains the fact that by increasing the subcarrier interval, theeffect due to frequency fluctuations can be reduced.

The subcarrier interval 1/2 Ta for N symbols in the 1 GHz band is:

1/2Ta=1/N

The subcarrier interval 1/2Tb for M symbols in the 2 GHz band is:

1/2Tb=1/M

Because N>M, as shown in the figure, the subcarrier interval 1/2Tb inthe 2 GHz band is larger than the subcarrier interval 1/2Ta in the 1 GHzband. Here, taking into consideration a case in which frequencyfluctuation over a frequency Δf occurs, by reason of broadening thesubcarrier interval, the leakage CT₂ with respect to the adjacentfrequency in the 2 GHz band is smaller than the leakage CT₁ with respectto the adjacent frequency in the 1 GHz band, and the effect of frequencyfluctuations can be reduced.

(B) First Embodiment

FIG. 6 shows the configuration of the transmission apparatus of a firstembodiment, in a radio communication system using a plurality ofdifferent radio frequencies, in which pilot lengths are made differentfor each radio frequency; FIG. 7 shows the configuration of a receptionapparatus.

In the transmission apparatus, the modulation portion 11 performs forexample QPSK modulation of the transmission data, the first pilotinsertion portion 12 inserts pilot signals PL1 for 1 GHz (see FIG. 1 andFIG. 2) generated by the pilot generation portion 13 into the QPSKin-phase component and quadrature component, and the 1 GHz transmitter14 up-converts the frequency of the signals with the pilots PL1 insertedto 1 GHz and transmits the signals from the antenna 15. The second pilotinsertion portion 16 inserts pilot signals PL2 for 2 GHz (see FIG. 1 andFIG. 2) generated by the pilot generation portion 13 into the QPSKin-phase component and quadrature component, and the 2 GHz transmitter17 up-converts the frequency of the signals with the pilots PL2 insertedto 2 GHz and transmits the signals from the antenna 18.

In the reception apparatus, the 1 GHz receiver 21 down-converts 1 GHzhigh-frequency signals received by the antenna 20 to baseband signalsand inputs the signals to the selection portion 22, and the 2 GHzreceiver 24 down-converts 2 GHz high-frequency signals received by theantenna 23 to baseband signals and inputs the signals to the selectionportion 22. The selection portion 22 selects the baseband signals outputfrom the receiver indicated by a 1 GHz/2 GHz selection signal SEL outputfrom a control portion, not shown, and inputs the selected signals tothe pilot extraction portion 25 and demodulation portion 27. The pilotextraction portion 25 extracts pilots (complex signals) from the inputsignals based on the 1 GHz/2 GHz selection signal SEL, and inputs theaveraging result to the channel estimation portion 26. The channelestimation portion 26 uses the input pilot signals and known pilotsignals to estimate the channel (path propagation characteristics). Thedemodulation portion 27 performs channel compensation of data signalsbased on the channel estimation value, and then demodulates thetransmission data.

In the case of FIG. 6, 1 GHz/2 GHz pilots PL1, PL2 are inserted into thesame transmission data and transmitted from the 1 GHz transmitter 14 and2 GHz transmitter 17, respectively; but as shown in FIG. 8, separatetransmission data 1, 2 can be modulated separately by modulators 11,11′, 1 GHz/2 GHz pilots PL1, PL2 inserted into the modulation results,and the signals transmitted by the 1 GHz transmitter 14 and 2 GHztransmitter 17 respectively. In this case, pilot insertion can beperformed before modulation. Further, the above are cases in which thepilot length is changed with each radio frequency, but a configurationis also possible in which the pilot length is changed for each band.

By means of the first embodiment, the pilot length or pilot interval ismade different in each band or at each radio frequency, so that thechannel estimation precision can be improved and reception performanceimproved in each band or at each frequency, and transmission efficiencycan be enhanced.

(C) Second Embodiment

FIG. 9 shows the configuration of the transmission apparatus in a secondembodiment in which guard interval lengths are made different in eachband, in a radio communication system in which OFDM transmission isperformed in each of a plurality of bands; FIG. 10 shows theconfiguration of a reception apparatus.

In the transmission apparatus, the serial/parallel conversion portion 31a of the multicarrier modulation portion 31 performs parallel conversioninto N-symbols of the transmission data, the IFFT portion 31 b performsIFFT processing as N subcarrier components of each of the parallel datasymbols, and the parallel/serial conversion portion 31 c converts theN-symbols of IFFT processing results (OFDM symbols) into series data asa OFDM symbol, which is output. The first guard interval additionportion 32 adds a guard interval (see FIG. 3) of the length for 1 GHzdesignated by the GI length designation portion 33 to the N-symbols(OFDM symbol), and the 1 GHz transmitter 34 up-converts the frequency ofthe signals with guard interval inserted to 1 GHz and transmits thesignals from the antenna 35. The second guard interval addition portion36 adds a guard interval (see FIG. 3) of the length for 2 GHz designatedby the GI length designation portion 33 to the N symbols (OFDM symbols)from the beginning, and the 2 GHz transmitter 37 up-converts thefrequency of the signals with guard interval inserted to 2 GHz andtransmits the signals from the antenna 38.

In the receiver, the 1 GHz receiver 41 down-converts the 1 GHzhigh-frequency received signals received by the antenna 40 to basebandsignals, which are input to the selection portion 44, and the 2 GHzreceiver 43 down-converts the 2 GHz high-frequency received signalsreceived by the antenna 42 to baseband signals, which are input to theselection portion 44. The selection portion 44 selects the basebandsignals output from the receiver indicated by a 1 GHz/2 GHz selectionsignal SEL from a control portion, not shown, and inputs the signals tothe guard interval removal portion 45. The guard interval removalportion 45 removes the 1 GHz or 2 GHz guard intervals from the inputsignals according to the 1 GHz/2 GHz selection signal SEL, and inputsthe result to the FFT portion 46. The FFT portion 46 performs parallelconversion into N-symbols of the input signals, then performs N-pointFFT processing, performs serial conversion of the FFT result, and inputsthe result to the demodulation portion 47. The demodulation portion 47demodulates the transmission data from the input signals.

In the case of FIG. 9, 1 GHz/2 GHz guard intervals G1, G2 are insertedinto the same OFDM symbols and transmitted by the 1 GHz transmitter 34and the 2 GHz transmitter 37; but as shown in FIG. 11, a configurationis possible in which multicarrier modulation of separate transmissiondata 1, 2 is performed by multicarrier modulators 31, 31′, 1 GHz/2 GHzguard intervals are respectively inserted into the OFDM symbols that arethe modulation results, and the data is transmitted by the 1 GHztransmitter 34 and 2 GHz transmitter 37.

The above are cases in which guard interval lengths are changed in eachof a plurality of bands; but guard interval lengths can also be changedat each carrier frequency in multicarrier transmission. FIG. 12 showsthe configuration of a transmission apparatus in such a multicarriertransmission system, in which guard interval lengths are changed at eachfrequency. Each of the single-carrier modulation portions 51 a to 51 nprovided on the multicarrier modulation portion 51 performs prescribedmodulation (for example QPSK modulation) of transmission data DATA1 toDATAn, the first to nth guard interval addition portions 52 a to 52 ninsert guard intervals G1 to Gn with prescribed lengths into therespective N modulated data symbols, based on the guard interval lengthsdesignated by the GI length designation portion 53, and the first to nthtransmitters 53 a to 53 n transmit the data, with the guard intervalsinserted, from the antennas 54 a to 54 n.

By means of the above second embodiment, by changing the lengths ofinserted guard intervals in each band or at each frequency, intersymbolinterference is reduced and reception performance improved in each bandor at each frequency, and transmission efficiency can be enhanced.

(D) Third Embodiment

FIG. 13 shows the configuration of a transmission apparatus in thirdembodiment, in a radio communication system which performs OFDMtransmission in each of a plurality of bands, in which the number ofsubcarriers is made different and the subcarrier interval is madedifferent in each band; FIG. 14 shows the configuration of a receptionapparatus.

The modulation portion 61 performs for example QPSK modulation oftransmission data and outputs complex data. In the first multicarriermodulation portion 62, the serial/parallel conversion portion 62 aconverts the transmission data into N parallel data symbols, the IFFTportion 62 b performs IFFT processing of the parallel data symbols as Nsubcarrier components, and a parallel/serial conversion portion, notshown, converts the N-symbol IFFT processing result (OFDM symbol) intoserial data, which is output. The first guard interval addition portion63 adds a guard interval of prescribed length to the N-symbols (OFDMsymbol), and the 1 GHz transmitter 64 up-converts the frequency of thesignals with guard intervals inserted to 1 GHz and transmits the signalsfrom the antenna 65. The guard interval addition portion 63 inserts theguard intervals of length for use at 1 GHz for example.

In the second multicarrier modulation portion 66, the serial/parallelconversion portion 66 a converts the transmission data into M paralleldata symbols (M<N), the IFFT portion 66 b performs IFFT processing ofthe parallel data symbols as M subcarrier components, and aparallel/serial conversion portion, not shown, converts the M-symbolIFFT processing result (OFDM symbols) into serial data, which is output.The second guard interval addition portion 67 adds a guard interval ofprescribed length to the M-symbols (OFDM symbol), and the 2 GHztransmitter 68 up-converts the frequency of the signals with guardintervals inserted to 2 GHz and transmits the signals from the antenna69. The guard interval addition portion 67 inserts the guard intervalsof length for use at 2 GHz for example.

In the receiver, the 1 GHz receiver 71 down-converts the 1 GHzhigh-frequency received signals received by the antenna 70 to basebandsignals and inputs the signals to the selection portion 74, and the 2GHz receiver 73 down-converts the 2 GHz high-frequency received signalsreceived by the antenna 72 to baseband signals and inputs the signals tothe selection portion 74. The selection portion 74 selects the basebandsignals output from the receiver indicated by a 1 GHz/2 GHz selectionsignal SEL output from a control portion, not shown, and inputs thesignals to the guard interval removal portion 75. The guard intervalremoval portion 75 deletes guard intervals of prescribed length from theinput signals, and inputs the result to the FFT portion 76. The FFTportion 76 performs N-point FFT processing when the 1 GHz/2 GHzselection signal SEL indicates 1 GHz, performs M-point FFT processingwhen 2 GHz is indicated, converts the FFT result to serial data, andinputs the data to the demodulation portion 77. The demodulation portion77 demodulates the transmission data from the input signals.

By means of the above third embodiment, by making the number of carriers(N, M) in multicarrier transmission different or making the subcarrierintervals different in each band, the effect of frequency fluctuationsin higher-frequency bands can be reduced and reception performanceimproved, and transmission efficiency can be enhanced.

In the above embodiments, one among the pilot length, guard intervallength, or subcarrier intervals was changed in each band or at eachfrequency; but a configuration is possible in which two or more arechanged simultaneously. That is, all of the combinations in which twoamong these three parameters are changed, or all combinations in whichall three are changed, can be adopted.

What is claimed is:
 1. A transmission apparatus in a radio communicationsystem which simultaneously uses a plurality of different radiofrequencies to transmit signals, comprising: a radio format settingportion, which is provided for each transmission frequency of theplurality of different radio frequencies and separately sets a radioformat of transmission signals for each transmission frequency; and atransmitter, which is provided for each transmission frequency of theplurality of different radio frequencies and transmits signals at eachof said transmission frequencies, wherein each radio format settingportion sets a pilot length of the transmission signals separately foreach transmission frequency of the plurality of different radiofrequencies.